&IF, &THEN, &ELSEIF, &ELSE, and &ENDIF preprocessor directives

These directives set logical conditions for the inclusion of blocks of code to compile.


&IF `expression` &THEN `block` [ &ELSEIF `expression` &THEN `block` ] ... [ ELSE `block` ] &ENDIF

An expression that can contain preprocessor name references, the operators listed in
Table 6, the ABL functions listed in Table 7, and the DEFINED( ) preprocessor function.

When it encounters an &IF directive, the preprocessor evaluates the expression that immediately follows. This expression can continue for more than one line; the &THEN directive indicates the end of the expression. If the expression evaluates to TRUE, then the block of code between it and the next &ELSEIF, &ELSE, or &ENDIF is compiled. If the expression evaluates to FALSE, the block of code is not compiled and the preprocessor proceeds to the next &ELSEIF, &ELSE, or &ENDIF directive. No include files referenced in this block of code are included in the final source. You can nest &IF directives.

The expression that follows the &ELSEIF directive is evaluated only if the &IF expression tests false. If the &ELSEIF expression tests TRUE, the block of code between it and the next &ELSEIF, &ELSE, or &ENDIF directive is compiled. If the &ELSEIF expression tests FALSE, the preprocessor proceeds to the next &ELSEIF, &ELSE, or &ENDIF directive.

The block of code between the &ELSE and &ENDIF directives is compiled only if the &IF expression and the &ELSEIF expressions all test false. If there are no &ELSEIF directives, the block of code is compiled if the &IF expression tests false.

Once any &IF or &ELSEIF expression evaluates to TRUE, no other block of code within the &IF...&ENDIF block is compiled.

The &ENDIF directive indicates the end of the conditional tests and the end of the final block of code to compile.

Table 5: Preprocessor expressions
Type of expression	TRUE	FALSE
LOGICAL	TRUE	FALSE
CHARACTER	non-empty	empty
INTEGER	non-zero	0
INT64	non-zero	0
DECIMAL	not supported	not supported

Table 6 lists the operators supported within preprocessor expressions. These operators have the same precedence as the regular ABL operators.

Table 6: Preprocessor operators
Operator	Description
+	Addition
-	Subtraction
*	Multiplication
/	Division
=	Equality
<>	Inequality
>	Greater than
<	Less than
=>	Greater than or equal to
<=	Less than or equal to
AND	Logical and
OR	Logical or
NOT	Logical not
BEGINS	Compares the beginning letters of two expressions
MATCHES	Compares two strings

Table 7: Functions allowed in preprocessor expressions
ABSOLUTE	ASC	AUDIT-ENABLED
DATE	DAY	DBTYPE
DECIMAL	ENCODE	ENTRY
ETIME	EXP	FILL
INDEX	INT64	INTEGER
KEYWORD	KEYWORDALL	LC
LEFT-TRIM	LENGTH	LIBRARY
LOG	LOOKUP	MATCHES
MAXIMUM	MEMBER	MINIMUM
MODULO	MONTH	NUM-ENTRIES
OPSYS	PROPATH	PROVERSION
RANDOM	REPLACE	RIGHT-TRIM
R-INDEX	ROUND	SQRT
STRING	SUBSTITUTE	SUBSTRING
TIME	TODAY	TRIM
TRUNCATE	WEEKDAY	YEAR

When the preprocessor evaluates expressions, all arithmetic operations are performed with integers. Preprocessor name references used in arithmetic operations must evaluate to integers.